1. Field of the Invention
The present invention relates to an apparatus and a method for controlling a sewing machine driven by a drive such as a motor.
2. Description of the Background Art
FIG. 62 is an arrangement diagram showing a conventional sewing machine controlling apparatus disclosed in Japanese Laid-Open Patent Publication No. HEI3-14479, for example. In this drawing, the numeral 1 indicates a sewing machine, 2 denotes a motor, 3 designates a needle position detector acting as needle position detection means to detect the needle position of the sewing machine 1, 4 represents a machine pulley, 5 indicates a motor pulley, and 6 represents a belt fitted over the machine pulley 4 and the motor pulley 5 to transmit the rotation of the motor 2 to the sewing machine 1. 7 designates a stator of the motor 2, 8 denotes a rotor of the motor 2, and 9 indicates a brake for stopping the motor 2. 10 denotes a foot pedal used to operate the sewing machine 1, 11 represents a lever unit which detects the operation of the foot pedal 10, 12 designates a sewing machine control circuit serving as machine control means to control the orientation, automatic thread trimming, backtacking, etc., of a machine needle, and 13 indicates a motor speed control circuit acting as motor speed control means to control the motor 2 and the brake 9, thereby providing desired stitching speed under the operation command of the foot pedal 10 and others.
S1 indicates a stitching start signal, S2 designates a thread trimmer start signal, S3 represents a needle UP signal, VC denotes a speed command signal, SRT indicates a run signal, BK represents a brake signal, LLKO denotes a low-speed command signal, IMCO designates a middle-speed command signal, and R indicates a reverse rotation signal. It is to be understood that the stitching start signal S1 and the thread trimmer start signal S2 are input signals from the lever unit 11 to the sewing machine control circuit 12, the speed command signal VC is an input signal from the lever unit 11 to the motor speed control circuit 13, and the run signal SRT, the brake signal BK, the low-speed command signal LLKO, the middle-speed command signal IMCO and the reverse rotation signal R are command signals from the sewing machine control circuit 12 to the motor speed control circuit 13.
The operation of the conventional apparatus arranged as described above will now be described. An operation timing chart is shown in FIG. 63. Toeing down the foot pedal 10 switches the stitching start signal S1 on, outputs the run signal SRT from the sewing machine control circuit 12 to the motor speed control circuit 13, excites the stator 7 of the motor 2, and rotates the rotor 8 to drive the sewing machine 1 via the motor pulley 5, the belt 6 and the machine pulley 4.
Then, by changing the toe-down amount of the foot pedal 10, the voltage, current and frequency applied by the motor speed control circuit 13 to the stator 7 of the motor 2 are under the control of the speed command signal VC of the lever unit 11 and the position detection signal FG of the needle position detector 3 fitted to the sewing machine 1 to control the speed of the sewing machine 1 to a desired value according to the toe-down amount of the foot pedal 10.
When the foot pedal 10 is returned to a neutral position, the low-speed command signal LLKO for positioning is output by the sewing machine control circuit 12, and simultaneously, the needle UP or DOWN of the sewing machine 1 is detected under the control of the position detection signal (UP or DOWN) of the needle position detector 3, and the magnetic brake 9 is excited to stop the sewing machine 1.
Further, when the foot pedal 10 is heeled, i.e., is turned in the direction opposite to the tow-down direction, the thread trimmer start signal S2 is switched on, the machine control circuit 12 outputs the run signal SRT and the middle-speed command signal IMCO to carry out end backtacking. After the end backtacking is finished, the middle-speed command signal IMCO is switched off, the low-speed command signal LLKO is switched on, and a thread trimmer output is provided to trim the machine threads.
The needle position detector 3 outputs the needle UP position signal UP and needle DOWN position signal DN which represent the positions of the machine needle. The outputs of this needle position detector 3 and the lever unit 11 are provided to the sewing machine control circuit 12 which exercises the speed control of the motor 2 and the control of various solenoids (not shown) of the sewing machine 1.
The motor speed control circuit 13, which contains an inverter, switches between phases to reverse the motor 2 for the following reason. In the automatic thread trimmer mechanism of the sewing machine 1, since the machine threads are typically trimmed using the rotation of the machine spindle after the machine needle has moved away from a material to be sewn, risen, and reached the highest position or a top dead center, the position where the sewing machine is braked to a stop after machine thread trimming and needle position detection is considerably lower than said top dead center. Hence, when the machine needle stops at this low position if the sewing machine rotates in a forward direction only, the material moved in/out, for example, is caught by the machine needle. To prevent this, the pedal 10 is operated to perform thread trimmer operation to cut the machine threads, the needle position is then detected, and the sewing machine is braked to a stop, whereby if the machine needle stops at the low position, the motor 2 is further reversed to return the machine needle nearer to the top dead center and stop there, and therefore, even a heavy material to be stitched is not caught by the machine needle. It is to be understood that when the machine needle is not at the UP position, the needle UP signal S3 is given to run the sewing machine forward to rotate the machine needle to the UP position. When the machine needle is not at the UP position at power-on, the sewing machine is run forward to rotate the machine needle to the UP position if the needle UP signal S3 is not provided.
The operation of the sewing machine control circuit 12 will now be described in accordance with FIG. 64. The sewing machine control circuit 12 consists of microprocessor circuits (not shown) such as a CPU, ROM, RAM and I/O ports, and is under the control of software. When the pedal 10 is toed down to provide the stitching start signal S1 to a run signal input circuit 301, the run signal SRT is output from a rotation/stop command circuit 305 to the motor speed control circuit 13 via a run control circuit 300 to start the motor 2 running.
Subsequently, when the pedal 10 is returned to the neutral position, the run control circuit 300 outputs the low-speed command signal LLKO to the motor speed control circuit 13 via a speed command circuit 304, whereby the motor 2 is controlled to run at low speed.
Detecting that the sewing machine 1 has reached or exceeded a predetermined speed via a needle UP/DOWN position input circuit 302 according to the pulse width of the needle DOWN position signal DN and that the needle DOWN position signal DN has entered, the run control circuit 300 switches the run signal SRT off and switches the brake signal BK on for a given period of time via the rotation/stop command circuit 305.
Then, when the pedal 10 is heeled to switch on the thread trimmer start signal S2, the middle-speed command signal IMCO is output via the run control circuit 300 and the speed command circuit 304, whereby the motor 2 runs at middle speed, backtacking is performed, the middle-speed command signal IMCO is then switched off, and further the low-speed command signal LLKO is switched on, causing the motor 2 to run at low speed. When the needle DOWN position signal DN is switched on, the thread trimmer output T is provided by a solenoid control circuit 303 to conduct automatic thread trimming of the sewing machine 1. When the needle UP position signal UP is detected, the run signal SRT is switched off, and the brake signal BK is switched on for a given length of time via the rotation/stop command circuit 305, the solenoid control circuit 303 switches the thread trimmer output T off and a wiper output W on for a given period of time, stopping the sewing machine at a thread take-up lever top dead center. It is to be understood that the thread take-up lever top dead center indicates that the thread take-up lever (not shown), which feeds the needle thread of the sewing machine 1, is at the top position, where the thread has been fed the most and cannot be removed from the machine needle at the start of next stitching.
After the brake signal BK has been excited for a given length of time, the reverse rotation signal R is switched on and the run signal SRT is switched on to reverse the motor 2. When the needle top dead center is detected using the needle UP position signal UP, the run signal SRT is switched off and the brake signal BK is switched on for a given period of time to stop the sewing machine at the needle top dead center, and the brake signal BK is switched off. Subsequently, when the thread trimmer start signal S2 is on, the solenoid control circuit 303 outputs a presser foot UP output FU to raise the presser foot (not shown).
FIG. 65 shows an example of needle bar motion, wherein a vertical axis represents the height of the machine needle with respect to a throat plate surface (0 mm) and a horizontal axis represents the rotary angle of an arm shaft (not shown) of the sewing machine 1. As the arm shaft of the sewing machine 1 rotates, the height of the machine needle changes.
At the position of 0 degrees in FIG. 65, for example, the machine needle is at the top dead center and is out of the material, whereby the material can be removed. At the position of 180 degrees, the machine needle is at the bottom dead center. When it is desired to change the direction of the material to change the stitching direction, the machine needle stopping at this position allows the material to be turned without being offset.
At the position of 90 degrees, the machine needle sticks in the material. At the position of 100 degrees, the machine needle is located at the position of the throat plate (not shown) where the material is placed. The machine needle comes out of the throat plate surface at the position of 260 degrees and comes out of the material at the position of 270 degrees.
The UP position signal UP of the machine needle is switched on slightly in front of the thread take-up lever top dead center (at 40 degrees) and the DOWN position signal DN of the machine needle is switched on slightly in front of the needle DOWN position (at 160 degrees). The machine needle is oriented to a stop at the needle UP or DOWN position under the control of these two signals.